Patent GB-1275681-A (GB)
Title: Line deflection stages
IPC: H04N3/16
Filed: 1970-02-18
Abstract: 1275681 EHT supplies PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 18 Feb 1970 [21 Feb 1969] 7807/70 Heading H2F [Also in Divisions H3-H4] A line time base generator adapted to maintain constant picture width comprises two generators for supplying the output current, the first being stabilized in dependence upon EHT voltage and component variations to maintain operation at or just above the saturation knee of the driving element and the other stabilized against supply voltage variations. By thus separating stabilizing functions the excess dissipation in one generator necessary to ensure correct operation at the lowest supply voltage may be avoided. Transistor and valve embodiments are described. A basic circuit shown in Fig. 1 comprises a main sawtooth generator 1 of the series booster resonant return type coupled by winding 8 to deflection coils 5. It is stabilized against EHT and component variations to operate close above a knee of the valve characteristic the circuit also comprises a similar auxiliary sawtooth current generator 2 supplying via winding 12 in series with winding 8 the same value of current to the deflection coils but stabilized in dependence upon the supply voltage. The EHT and the deflection current are however allowed to vary slightly in such ratio that the picture width remains constant. Fig. 11 (not shown) is a similar transistorized circuit but in this case the main transistor is stabilized to operate in switching mode along the knee of the saturation region. Stabilization is effected in the main generator 1 of Fig. 2 by a non-linear element 23 arranged to rectify the line flyback voltage, the rectified voltage, representing the EHT value, being adjustable by means of resistor 24<SP>11</SP> to provide a desired amount of EHT variation. Adjustment close above the knee of the valve is effected by a potentiometer 24<SP>1</SP> deriving a voltage from the boost capacitor. The auxiliary generator 12 is stabilized by applying supply voltage to the grid of a stabilizer valve 26 and by a non-linear resistor connected to the cathode, the valve supplying bias to the auxiliary generator. Flyback pulses, representing the deflection current of each generator are combined via windings 36 and 38 to provide further stabilization, adjustment of the relative contributions to the output being effected by a potentiometer 37. As the component so produced from the main generator varies with EHT voltage a compensating voltage is fed from the EHT circuit 40 into the grid of the stabilizer valve. Resistor 39t adjusts the ratio of deflection current variation to supply voltage variation. A transistor or rectifier may replace the stabilizer valve (Figs. 5, 7 and 9, not shown) a capacitor 31 couples supply voltage transients to the grid of the stabilizer so as to speed the response to changes in supply voltage and a protective clamping diode connected to the grid of the auxiliary driver valve (Fig. 8, not shown) may also rectify the drive to the grid so as to stabilize the generator against input and signal amplitude variations. East to West pin cushion correction is effected in Fig. 1 by applying the deflection waveform to the grid of the stabilizer valve via an integrator 30, 31. A correction voltage may alternatively be applied to the cathode of the stabilizer valve or to the base of a transistor replacing the valve (Figs. 5, 7 and 8, not shown). Protection of the transistor may be affected by diodes (Fig. 8). Alternatively the stabilizer valve may be replaced by a rectifier circuit (Fig. 6, not shown). Coupling the generators together in Fig. 2 is effected by series output windings 8, 12 and a compensating winding 10 (which alternatively may be connected between taps on the winding) to prevent coupling between the generator output circuits. In Fig. 1 a hybrid transformer couples the generators (1, 2) to the deflection coil (5) and a balancing coil (10) is connected to the balancing winding of the transformer. The deflection coils may be in parallel or in series (5<SP>1</SP>, 5<SP>11</SP>, Figs. 9 and 10, not shown). Anisotropic stigmatism at the picture corners is corrected by a modulating wave applied differentially to the deflection coils at 17. S correction is effected by a capacitor 19. When series coils are used a pair of capacitors may be provided (19<SP>1</SP>, 19<SP>11</SP>, Fig. 9, not shown) but this may be avoided by using an inductive centre tap (45<SP>1</SP>, 45<SP>11</SP>, Fig. 10, not shown). Centering is effected by a rectifier supply 21 (also in Fig. 10, not shown). The EHT winding is tuned to the flyback and harmonic frequencies the capacitor 15 representing the inter-winding capacitance. The auxiliary generator is similarly tuned. The filament supply for the CR tube, boost diode and EHT rectifier may be obtained from the auxiliary generator since this is not loaded by the EHT supply. CR tube second grid supply is obtained from a rectifier 25 connected to the output transformer of the main generator so that this supply varies in proportion to the EHT supply. Convergence voltages are obtained from resistor 22 connected to winding 7. The field time base supply is available at 45 from winding 7 or jointly from the generator. Its value varies proportionally to the line deflection current.